The present invention relates to polyester resin compositions having improved physical characteristics, particularly improved impact strength and superior moldability, for example, injection moldability.
Polyethylene terephthalate (hereinafter referred to as PET) exhibits excellent heat resistance, chemical resistance, mechanical properties and electrical properties and had been used in many industrial products in the form of fibers, films and the like. Particularly, PET reinforced by inorganic fillers such as glass fibers possesses remarkably improved thermal and mechanical properties and is currently widely used in such applications as engineering plastics.
However, PET and filler-reinforced PET are not fully satisfactory in terms of the impact resistance of shaped articles and they sometimes present problems as the shaped articles chip or break in the course of manufacture, during transportation, or in use of the final products. With respect to impact resistance, PET is even inferior to poly1,4-butylene terephthalate) (hereinafter referred to as PBT) which is also a thermoplastic polyester.
The method commonly practiced for improving the impact resistance of PET or filler-reinforced PET is blending certain elastomeric polymers with PET.
For example Japanese Patent Publication No. 26223/1970 describes a copolymer of a saturated aliphatic monocarboxylic acid vinyl ester with an .alpha.-olefin as an impact resistance-improving agent for polyester resins. Japanese Patent Publication No. 26224/1970 teaches a copolymer of an acrylic acid ester with a conjugated diene compound as an impact resistance-improving agent for polyester resins. The polyester impact resistance-improving agent described in Japanese Patent Publication No. 26225/1970 is an ionomer. However, even shaped articles manufactured by such techniques are not fully satisfactory in impact resistance.
Also known are other methods for improving the impact resistance of polyester resins. For example, Japanese Patent Application Laid-Open Nos. 51-144452, 52-32045, and 53-117049 describe the technique of blending polyester resins with a coplymer of an .alpha.-olefin with an .alpha.,.beta.-unsaturated carboxylic acid glycidyl ester. The technique in which an ethylenic copolymer is further added as a third component to the above-mentioned copolymer is disclosed in Japanese Patent Application Nos. 58-17148 and 58-17151, and a similar technique using polyphenylene sulfide as a third component is disclosed in Japanese Patent Application Laid-Open No. 57-92044.
Even by these improved techniques, PET has not attained sufficient impact strength.
Among various plastics, aromatic polycarbonates are known to have a high impact resistance, and many years ago a first attempt was made to blend such a polycarbonate resin with PET (Japanese Patent Publication 14035/1961). Recent patent literature, for example, U.S. Pat. No. 4,257,937, discloses a combination of a polyacrylate resin and an aromatic polycarbonate resin as an impact resistance-improving agent for polyester resins. This technique helped attain a fairly high impact resistance. In addition, Japanese Patent Application Laid-Open No. 59-161460 showed that in improving the impact resistance of PET by using a polyacrylate resin and an aromatic polycarbonate resin, a further combination with an effective amount of a poly1,4-butylene terephthalate) results in a further remarkable improvement in the impact resistance. Even by this technique, however, the impact resistance (Izod impact strength) of the article is at best no more than approximating that of the PBT/polyacrylate resin/aromatic polycarbonate resin composition and does not exceed the impact resistance exhibited thereby.
Regarding filler-reinforced polyester resins, blending a polyester with a very large proportion of elastomer will result in an improved impact strength (for example, Japanese Patent Publication No. 30742/1984) but the addition of such a large amount of elastomer detracts from the heat resistance and mechanical properties of the resin composition.
Japanese Patent Application Laid-Open No. 53-102360 teaches a technique of blending PBT with PET type filler-reinforced polyester to improve the warpage resistance of the polyester. However, blending PBT with a PET type filler-reinforced polyester does not contribute to its impact strength.